Porous interlayer for a lithium-sulfur battery

ABSTRACT

A porous interlayer for a lithium-sulfur battery includes an electronic component and a negatively charged or chargeable lithium ion conducting component. The electronic component is selected from a carbon material, a conductive polymeric material, and combinations thereof. In an example, the porous interlayer may be disposed between a sulfur-based positive electrode and a porous polymer separator in a lithium-sulfur battery. In another example, the porous interlayer may be formed on a surface of a porous polymer separator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/052,032, filed Oct. 11, 2013, now U.S. Pat. No. 9,373,829, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to a porous interlayer for alithium-sulfur battery.

BACKGROUND

Secondary, or rechargeable, lithium-sulfur batteries are often used inmany stationary and portable devices, such as those encountered in theconsumer electronic, automobile, and aerospace industries. The lithiumclass of batteries has gained popularity for various reasons including arelatively high energy density, a general nonappearance of any memoryeffect when compared to other kinds of rechargeable batteries, arelatively low internal resistance, and a low self-discharge rate whennot in use. The ability of lithium batteries to undergo repeated cyclingover their useful lifetimes makes them attractive and dependableelectrical energy storage devices.

SUMMARY

A porous interlayer for a lithium-sulfur battery includes an electroniccomponent and a negatively charged or chargeable lithium ion conductingcomponent. The electronic component is selected from a carbon material,a conductive polymeric material, and combinations thereof. In anexample, the porous interlayer may be disposed between a sulfur-basedpositive electrode and a porous polymer separator in a lithium-sulfurbattery. In another example, the porous interlayer may be formed on asurface of a porous polymer separator.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent byreference to the following detailed description and drawings, in whichlike reference numerals correspond to similar, though perhaps notidentical, components. For the sake of brevity, reference numerals orfeatures having a previously described function may or may not bedescribed in connection with other drawings in which they appear.

FIG. 1A is a schematic, cross-sectional view of an example of a freestanding porous interlayer including a fibrous electronic component anda negatively charged lithium ion conducting component bound thereto;

FIG. 1B is a schematic, cross-sectional view of another example of afree standing porous interlayer including a porous electronic componentand the negatively charged lithium ion conducting component boundthereto;

FIG. 2 is a schematic, perspective view of an example of alithium-sulfur battery showing a charging and discharging state, thebattery including an example of the porous interlayer according to thepresent disclosure;

FIG. 3 is a scanning electron microscope (SEM) image of an example ofthe free standing porous interlayer formed with carbon nanotubes and anegatively chargeable sulfonated tetrafluoroethylene basedfluoropolymer-copolymer;

FIG. 4 is a graph illustrating the charge capacity and dischargecapacity (mAh/g_(S)) for comparative battery cells including nointerlayer or a carbon interlayer, and for an example battery cellincluding an interlayer according to the present disclosure;

FIG. 5 a graph illustrating the Coulombic efficiency (%) for thecomparative battery cells including no interlayer or the carboninterlayer, and for the example battery cell including the exampleinterlayer according to the present disclosure; and

FIG. 6 is a graph depicting the voltage (V) profile in the 2^(nd) cyclefor the comparative battery cells including no interlayer or the carboninterlayer, and for the example battery cell including the exampleinterlayer according to the present disclosure.

It is to be understood that the components shown in FIG. 2 are depictedto illustrate the flow of lithium ions between the negative and positiveelectrodes of the lithium-sulfur battery, and thus are not necessarilydrawn to scale.

DETAILED DESCRIPTION

Lithium-sulfur batteries generally operate by reversibly passing lithiumions between a negative electrode (sometimes called an anode) and apositive electrode (sometimes called a cathode). The negative andpositive electrodes are situated on opposite sides of a porous polymerseparator soaked with an electrolyte solution that is suitable forconducting the lithium ions. Each of the electrodes is also associatedwith respective current collectors, which are connected by aninterruptible external circuit that allows an electric current to passbetween the negative and positive electrodes.

It has been found that the lithium-sulfur battery life cycle may belimited by the migration, diffusion, or shuttling of polysulfides fromthe sulfur cathode during the battery discharge process, through theporous polymer separator, to the anode. The S_(X) polysulfides generatedat the cathode are soluble in the electrolyte, and can migrate to theanode (e.g., a lithium electrode) where they react with the anode in aparasitic fashion to generate lower-order polysulfides. Theselower-order polysulfides diffuse back to the cathode and regenerate thehigher forms of polysulfide. As a result, a shuttle effect takes place.This shuttle effect leads to decreased sulfur utilization,self-discharge, poor cycleability, and reduced Coulombic efficiency ofthe battery. It is believed that even a small amount of polysulfide atthe anode can lead to parasitic loss of active lithium at the anode,which prevents reversible electrode operation and reduces the usefullife of the lithium-sulfur battery.

In the examples disclosed herein, the diffusive polysulfide of thelithium-sulfur battery may be mitigated by incorporating a porousinterlayer between the porous polymer separator and the cathode of thelithium-sulfur battery. The porous interlayer includes an electroniccomponent for conducting electrons and a negatively charged componentfor conducting lithium ions while repelling polysulfides. In addition toreducing or eliminating the shuttle effect, the porous interlayer alsoimproves the utilization of active materials within the lithium-sulfurbattery. This can lead to the lithium-sulfur battery exhibiting enhancedcapacity, and thus a long useful life. The lithium-sulfur batterydisclosed herein also maintains the sulfur cathode plateau voltagewithout sacrificing energy density, and exhibits a small internalresistance.

Referring now to FIGS. 1A and 1B, two examples of the porous interlayer10 and 10′ are schematically depicted. Each of the porous interlayers10, 10′ includes some form of the electronic component 12 or 12′, anegatively charged (or chargeable) component 14 interspersed among andbound to the electronic component 12 or 12′, and pores 16 or pores 16and 17. As illustrated, the electronic component 12, 12′ is capable ofconducting electrons (denoted “e” in FIGS. 1A and 1B) and the negativelycharged component 14 is capable of conducting lithium ions (denoted “+”in FIGS. 1A and 1B).

The electronic component 12, 12′ may be in any form, such as nanofibers,nanotubes (i.e., a cylindrical nanostructure), hollow spheres, porousmaterials, or the like. In the example shown in FIG. 1A, the electroniccomponent 12 is a network of nanofibers, nanotubes, or some otherstructure having a length-to-diameter ratio of up to 132,000,000:1. Inthe example shown in FIG. 1B, the electronic component 12′ is a porousmaterial (e.g., a material having internal pores 17).

The electronic component 12, 12′ may be carbon, a conductive polymericmaterial, or combinations thereof. Examples of suitable carbonelectronic components 12, 12′ include carbon nanotubes, graphene,microporous carbon, mesoporous carbon, and carbon hollow spheres.Combinations of the various carbon electronic components 12, 12′ mayalso be used. The graphene may be used in any suitable form, such aspreformed sheets, nanoparticles, fibers, or any other commerciallyavailable form. Examples of suitable electrically conductive polymersinclude polyacetylene, polyphenylene vinylene, polypyrrole,polythiophene, polyaniline, and polyphenylene sulfide. Combinations ofthe various electrically conductive polymers may also be used. In anexample, the conductive polymeric material 12, 12′ includes nanofibers,nanotubes, hollow spheres, or combinations thereof made of any of thepreviously listed conductive polymers. The carbon hollow spheres or theconductive polymeric hollow spheres may have a particle size rangingfrom about 1 nm to about 100 μm.

The porous interlayer 10, 10′ also includes the negatively charged orchargeable component 14. As illustrated in FIGS. 1A and 1B, thecomponent 14 is negatively charged. When forming the porous interlayer10, 10′, it is to be understood that a negatively charged polymer or anegatively chargeable polymer may be used. The negatively chargedpolymers that are used in the examples disclosed herein are inherentlynegatively charged and lithium ion conductive. Examples of this type ofpolymer include polysulfone based-, polyether based-, or polysiloxanebased-single lithium ion conductive polymers. In contrast, thenegatively chargeable polymers are not inherently negatively charged orlithium ion conductive. Rather, these negatively chargeable polymers i)dissociate into negatively charged polymer backbones and cations in theelectrolyte of the lithium-sulfur battery, and ii) become lithium ionconductive through ion exchange with lithium ions in the electrolyte.Examples of the negatively chargeable polymers include a sulfonatedtetrafluoroethylene based fluoropolymer-copolymer (which is commerciallyavailable under the tradename NAFION®, E.I. Du Pont de Nemours and Co.Corp.), polyacrylic acid, or sodium alginate.

Whether the charged component or the chargeable component is used toform the porous interlayer 10, 10′, it is to be understood that when theporous interlayer 10, 10′ is used in the lithium-sulfur battery, thecomponent 14 is or becomes negatively charged and lithium ionconducting. This negatively charged component 14 is capable ofconducting lithium ions and is also capable of repelling polysulfides.

The pores 16 or pores 16 and 17 may also contribute to the lithium ionconducting properties and the polysulfide ion blocking properties of theporous interlayer 10, 10′. For example, the pores 16 or pores 16 and 17may be sized i) to allow the lithium ions to pass through, and ii) totrap the polysulfide ions and prevent them from passing through. In anexample, the porosity of the porous interlayer 10, 10′ is greater than0% and is equal to or less than 50%. In another example, the porosity ofthe porous interlayer 10, 10′ ranges from about 10% to about 40%. Theporosity of the porous interlayer 10, 10′ may depend, at least in part,on the thickness of the porous interlayer 10, 10′. In general, it isbelieved that the thicker the porous interlayer 10, 10′, the greaterblocking effect the porous interlayer 10, 10′ has due, at least in part,to the larger amount of trapping/blocking sites (i.e., pores 16 or pores16 and 17).

The thickness of the porous interlayer 10, 10′ may range from 10 nm toabout 1000 μm.

It is believed that any amount of the two components (i.e., theelectronic component 12, 12′ and the negatively charged or chargeablecomponent 14) may be used to form the porous interlayer 10, 10′. Theratio of the electronic component 12, 12′ to the negatively charged orchargeable component 14 may range anywhere from 1:99 to 99:1. In anexample, the porous interlayer 10, 10′ includes 5 wt % or less of thenegatively charged or chargeable component 14 and 95 wt % or more of theelectronic component 12, 12′.

The porous interlayer 10, 10′ may be formed as a free standing film (asshown in FIGS. 1A, 1B, and 3) or may be formed on a surface of a porouspolymer membrane (as shown in FIG. 2). Examples of the methods formaking these structures will now be described.

In an example of the method, two different dispersions are prepared andare exposed separately to a porous support structure. Examples of theporous support structure include a polytetrafluoroethylene (PTFE) film,a polyethylene (PE) membrane, a polypropylene (PP) membrane, a membraneincluding a blend of PE and PP, multi-layered structured porous films ofPE and PP, polyamides (Nylons), polycarbonate, or porous ceramics.Commercially available porous polymer membranes that are suitable forthe porous support structure include single layer polypropylenemembranes, such as CELGARD 2400, CELGARD 2500, and CELGARD 2325 fromCelgard, LLC (Charlotte, N.C.). When the free standing porous interlayer10, 10′ is to be formed, the PTFE porous support structure may bedesirable because it can be readily removed from the porous interlayer10, 10′. When the porous interlayer 10, 10′ coating is to be formed, anyof the listed membranes or materials may be desirable support structuresbecause these membranes and films can remain in the separator that isformed.

In this example of the method, one of the dispersions includes theelectronic component 12 and a first liquid, such as chloroform,methanol, tetrahydrofuran, etc. In an example, 20 mg of carbon nanotubesare dispersed in 20 mL of chloroform under ultrasonication at roomtemperature (e.g., ranging from about 18° C. to about 25° C.). Theelectronic component 12, 12′ may be added to the first liquid and thestirred to form the dispersion. The dispersion may be poured into theporous support structure. As the first liquid filters through the poresof the porous support structure, the electronic component 12, 12′ willremain on the surface.

In this example of the method, the other of the dispersions includes thenegatively charged or chargeable component 14 and a second liquid, suchas methanol. As an example, 20 mL of 0.5 wt % NAFION® in methanol may beused as the second dispersion. The negatively charged or chargeablecomponent 14 may be added to the second liquid and the stirred to formthe other dispersion. The other dispersion may be poured into the poroussupport structure having the electronic component 12, 12′ thereon. Asthe second liquid filters through the pores of the porous supportstructure, the negatively charged or chargeable component 14 will remainon the surface and bind to the electronic component 12, 12′.

The porous support structure may then be removed, resulting in theformation of the free standing interlayer 10, 10′. Alternatively, theporous support structure may be allowed to remain, resulting in acoating of the interlayer 10, 10′ formed on the porous supportstructure. This latter example forms a separator that includes theporous interlayer 10, 10′.

In another example of the method, a single dispersion is prepared. Inone example, separate dispersions respectively containing a liquid andthe electronic component 12, 12′, and a liquid and the negativelycharged or chargeable component 14 are prepared first, and then aremixed together to form the single dispersion. In another example, asingle liquid is used and the electronic component 12, 12′ and thenegatively charged or chargeable component 14 are both added to thesingle liquid. Any of the liquids previously described may be used.

The single dispersion may be poured into the porous support structure.As the liquid filters through the pores of the porous support structure,the electronic component 12, 12′ and a portion of the negatively chargedor chargeable component 14 will remain on the surface of the poroussupport structure. In these examples, the negatively charged orchargeable component 14 may bind to the electronic component 12, 12′within the single dispersion.

In this example of the method, the porous support structure may then beremoved, resulting in the formation of the free standing porousinterlayer 10, 10′. Alternatively, the porous support structure may beallowed to remain, resulting in a coating of the porous interlayer 10,10′ formed on the porous support structure.

In either example of the method, it is to be understood that the pouringof the dispersion(s) may be repeated as many times as is desirable inorder to increase the thickness of the porous interlayer 10, 10′.

It is also to be understood that when the porous support structureremains in contact with the porous interlayer 10, 10′ to form aseparator, some of the electronic component 12, 12′ and the negativelycharged or chargeable component 14 may penetrate the outermost pores ofthe porous support structure.

Referring now to FIG. 2, an example of the lithium-sulfur battery 20 isdepicted including an example of the porous interlayer 10, 10′ disclosedherein. In this example, the separator 27 of the battery 20 includes aporous polymer membrane 26 (which is also, in this example, the poroussupport structure used in the method) and the porous interlayer 10, 10′formed as a porous coating on a surface thereof. As illustrated, theseparator 27 is positioned within the lithium-sulfur battery so that theporous interlayer 10, 10′ faces a positive electrode 24. The separator27, which operates as both an electrical insulator and a mechanicalsupport, is sandwiched between a negative electrode 22 and the positiveelectrode 24 to prevent physical contact between the two electrodes 22,24 and to prevent the occurrence of a short circuit.

While not shown, it is to be understood that in another example of thelithium-sulfur battery 20, the free standing porous interlayer 10, 10′is not attached to the porous polymer membrane 26 but rather is a freestanding film that is positioned between the porous polymer membrane 26and the positive electrode 24. In this other example, any porous polymermembrane 26 that functions as a separator may be used.

As shown in FIG. 2, the lithium-sulfur battery 20 includes the negativeelectrode 22, the positive electrode 24, and the separator 27 positionedbetween the negative electrode 22 and the positive electrode 24. Thelithium-sulfur battery 20 also includes an interruptible externalcircuit 28 that connects the negative electrode 22 and the positiveelectrode 24.

Each of the negative electrode 22, the positive electrode 24, and theseparator 27 (including the porous interlayer 10, 10′) are soaked in anelectrolyte solution that is capable of conducting lithium ions. Aspreviously discussed, when the negatively chargeable component 14 isused the electrolyte also renders the component 14 negatively chargedand lithium conductive. The presence of the electrolyte solution mayalso provide a larger contact surface for lithium ion transport and mayenhance the conductivity of the positive electrode 24. While thepolysulfides may dissolve in the electrolyte at the positive electrode24, they are prevented from passing through the separator 27 due to theporous interlayer 10, 10′.

Any appropriate electrolyte solution that can conduct lithium ionsbetween the negative and positive electrode 22, 24 may be used in thelithium-sulfur battery 20. In one example, the non-aqueous electrolytesolution may be an ether based electrolyte that is stabilized withlithium nitrate. Other non-aqueous liquid electrolyte solutions mayinclude a lithium salt dissolved in an organic solvent or a mixture oforganic solvents. Examples of lithium salts that may be dissolved in theether to form the non-aqueous liquid electrolyte solution includeLiClO₄, LiAlCl₄, LiI, LiBr, LiSCN, LiBF₄, LiB(C₆H₅)₄, LiAsF₆, LiCF₃SO₃,LiN(FSO₂)₂, LiN(CF₃SO₂)₂, LiAsF₆, LiPF₆, and mixtures thereof. The etherbased solvents may be composed of cyclic ethers, such as 1,3-dioxolane,tetrahydrofuran, 2-methyltetrahydrofuran, and chain structure ethers,such as 1,2-dimethoxyethane, 1-2-diethoxyethane, ethoxymethoxyethane,tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycoldimethyl ether (PEGDME), and mixtures thereof.

The negative electrode 22 may include any lithium host material that cansufficiently undergo lithium plating and stripping while functioning asthe negative terminal of the lithium-sulfur battery 20. The negativeelectrode 22 may also be a silicon-based material that is prelithiated.For lithium ion cells, the negative electrode 22 may also include apolymer binder material to structurally hold the lithium host materialtogether. For example, the negative electrode 22 may be formed of anactive material, made from graphite or a low surface area amorphouscarbon, intermingled with a binder, made from polyvinylidene fluoride(PVdF), an ethylene propylene diene monomer (EPDM) rubber, sodiumalginate, or carboxymethyl cellulose (CMC). These materials may be mixedwith a high surface area carbon, such as acetylene black, to ensureelectron conduction between a current collector 22 a and the activematerial particles of the anode 22. Graphite is widely utilized to formthe negative electrode because it exhibits reversible lithiumintercalation and deintercalation characteristics, is relativelynon-reactive, and can store lithium in quantities that produce arelatively high energy density. Commercial forms of graphite that may beused to fabricate the anode 22 are available from, for example, TimcalGraphite & Carbon (Bodio, Switzerland), Lonza Group (Basel,Switzerland), or Superior Graphite (Chicago, Ill.). Other materials canalso be used to form the negative electrode including, for example,lithium titanate. The negative-side current collector 22 a may be formedfrom copper or any other appropriate electrically conductive materialknown to skilled artisans.

The positive electrode 24 of the lithium-sulfur battery 20 may be formedfrom any sulfur-based active material that can sufficiently undergolithiation and delithiation while functioning as the positive terminalof the lithium-sulfur battery 20. Examples of sulfur-based activematerials include S₈, Li₂S₈, Li₂S₆, Li₂S₄, Li₂S₂, and Li₂S. The positiveelectrode 24 may also include a polymer binder material to structurallyhold the sulfur-based active material together. The polymeric binder maybe made of at least one of polyvinylidene fluoride (PVdF), polyethyleneoxide (PEO), an ethylene propylene diene monomer (EPDM) rubber, orcarboxymethyl cellulose (CMC)). The positive-side current collector 14 amay be formed from aluminum or any other appropriate electricallyconductive material known to skilled artisans.

The negative-side current collector 22 a and the positive-side currentcollector 24 a may be positioned in contact with the negative electrode22 and the positive electrode 24, respectively, to collect and move freeelectrons to and from the external circuit 28.

The lithium-sulfur battery 20 may support a load device 30 that can beoperatively connected to the external circuit 28. The load device 30receives a feed of electrical energy from the electric current passingthrough the external circuit 28 when the lithium-sulfur battery 20 isdischarging. While the load device 22 may be any number of knownelectrically-powered devices, a few specific examples of apower-consuming load device include an electric motor for a hybridvehicle or an all-electrical vehicle, a laptop computer, a cellularphone, and a cordless power tool. The load device 22 may also, however,be an electrical power-generating apparatus that charges thelithium-sulfur battery 20 for purposes of storing energy. For instance,the tendency of windmills and solar panels to variably and/orintermittently generate electricity often results in a need to storesurplus energy for later use.

The lithium-sulfur battery 20 can include a wide range of othercomponents that, while not depicted here, are nonetheless known toskilled artisans. For instance, the lithium-sulfur battery 20 mayinclude a casing, gaskets, terminals, tabs, and any other desirablecomponents or materials that may be situated between or around thenegative electrode 22 and the positive electrode 24 forperformance-related or other practical purposes. Moreover, the size andshape of the lithium-sulfur battery 20, as well as the design andchemical make-up of its main components, may vary depending on theparticular application for which it is designed. Battery-poweredautomobiles and hand-held consumer electronic devices, for example, aretwo instances where the lithium-sulfur battery 20 would most likely bedesigned to different size, capacity, and power-output specifications.The lithium-sulfur battery 20 may also be connected in series and/or inparallel with other similar lithium-sulfur batteries 20 to produce agreater voltage output and current (if arranged in parallel) or voltage(if arranged in series) if the load device 20 so requires.

The lithium-sulfur battery 20 can generate a beneficial electric currentduring battery discharge (shown by reference numeral 21 in FIG. 2).During discharge, the chemical processes in the battery 20 includedelithiation from the surface of the negative electrode 22 andincorporation of the lithium cations into alkali metal polysulfide salts(i.e., Li₂S_(X)). As such, lithium polysulfides are formed (sulfur isreduced) on the surface of the positive electrode 24 in sequence (e.g.,S₈, Li₂S₈, Li₂S₆, Li₂S₄, Li₂S₃, Li₂S₂, Li₂S) while the battery 20 isdischarging. The chemical potential difference between the positiveelectrode 24 and the negative electrode 22 (ranging from approximately1.5 to 3.0 volts, depending on the exact chemical make-up of theelectrodes 22, 24) drives electrons produced by the delithiation at thenegative electrode 22 through the external circuit 28 towards thepositive electrode 24. The resulting electric current passing throughthe external circuit 28 can be harnessed and directed through the loaddevice 30 until the lithium in the negative electrode 22 is depleted andthe energy of the lithium-sulfur battery 20 is diminished.

The lithium-sulfur battery 20 can be charged at any time by applying anexternal charger to the lithium-sulfur battery 20 to reverse theelectrochemical reactions that occur during battery discharge. Duringcharging (shown at reference numeral 23 in FIG. 2), lithium plating tothe negative electrode 22 takes place and sulfur formation at thepositive electrode 24 takes place. The connection of an external chargerto the lithium-sulfur battery 20 compels the otherwise non-spontaneousoxidation of lithium sulfides at the positive electrode 24 to produceelectrons and free lithium cations. The electrons, which flow backtowards the negative electrode 22 through the external circuit 28, andthe lithium ions (Li⁺), which are carried by the electrolyte across the27 back towards the negative electrode 22, reunite at the negativeelectrode 22, and replenish the negative electrode 22 with lithium forconsumption during the next battery discharge cycle. The externalcharger that may be used to charge the lithium-sulfur battery 20 mayvary depending on the size, construction, and particular end-use of thelithium-sulfur battery 20. Some suitable external chargers include abattery charger plugged into an AC wall outlet and a motor vehiclealternator.

To further illustrate the present disclosure, examples are given herein.It is to be understood that these examples are provided for illustrativepurposes and are not to be construed as limiting the scope of thepresent disclosure.

Example 1

An example of the free standing porous interlayer was prepared usingcarbon nanotubes and NAFION®. A dispersion of carbon nanotubes was madein chloroform under ultrasonication, and the dispersion was pouredthrough a PTFE support structure. A second dispersion of NAFION® inmethanol was then filtered through the PTFE support structure. Thestructure was allowed to dry. The PTFE support structure was peeledaway, leaving the free standing porous interlayer shown in FIG. 3 (whichis a SEM image). This porous interlayer included less than 5 wt % of theNAFION®. The average aperture/pore size of this porous interlayer wassub-micron and the thickness was about 50 μm. Energy dispersive X-rayspectroscopy was used to identify the NAFION®, which is marked in FIG.3.

Example 2

Three coin cells (i.e., half cells) were prepared. Each of the coincells were composed of a lithium metal anode, a porous separator, and asulfur cathode. The first comparative coin cell included no porousinterlayer (referred to as “Comparative Example 1” or “1”). The secondcomparative coin cell included a 50 μm-thick carbon nanofiber porousinterlayer between the sulfur cathode and the porous separator (referredto as “Comparative Example 2” or “2”). The third example coin cellincluded the example of the porous interlayer formed in Example 1between the sulfur cathode and the porous separator (referred to as“Example 3” or “3”).

The coin cells were assembled in an argon-filled glove box. Theelectrolyte was 1M LiTFSI salt in dioxolane/1,2-dimethoxyethane(DIOX:DME) plus 2 wt. % LiNO₃. Galvanostatic charge and discharge cycletests were carried out at 25° C. between 2.85 V and 1.5 V.

FIG. 4 illustrates the charge (↑) and discharge (↓) curves for each ofthe comparative examples 1 and 2 and example 3. As illustrated, example3 (including the electronic and ionic conducting porous interlayerdisclosed herein) illustrated the best charge and discharge capacity (Cin FIG. 4, mAh/g_(S)) with a desirable cycle time (# in FIG. 4). Whilecomparative examples 1 and 2 exhibited desirably long cycle times, thecharge and discharge capacities were much worse than example 3. As such,these results indicate that the porous interlayer disclosed hereinsignificantly improves the cycling stability.

FIG. 5 illustrates the Coulombic efficiency (%) of comparative examples1 and 2 and example 3 at the various cycles (#). The high Coulombicefficiency exhibited by example 3 indicates that the polysulfideshuttling can be effectively suppressed by the porous interlayerdisclosed herein.

FIG. 6 illustrates the voltage profile (i.e., voltage, V, versuscapacity, C (mAh/g_(S))) for the second cycle of each of comparativeexamples 1 and 2 and example 3. From these results, it can be concludedthat the inclusion of the porous interlayer in example 3 maintains theplateau voltage and improves the utilization of active materials, whichresults in a higher energy density.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range of 5 wt % or less should be interpreted to include notonly the explicitly recited limits of 5 wt % or less, but also toinclude individual values, such as 4.75 wt %, 3 wt %, 2.3 wt %, etc.,and sub-ranges, such as from about 0.5 wt % to about 4.5 wt %; fromabout 1 wt % to about 3.5 wt %, etc. Furthermore, when “about” isutilized to describe a value, this is meant to encompass minorvariations (up to +/−5%) from the stated value.

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

While several examples have been described in detail, it is to beunderstood that the disclosed examples may be modified. Therefore, theforegoing description is to be considered non-limiting.

What is claimed is:
 1. A method for making a porous interlayer for alithium-sulfur battery, the method comprising; dispersing an electroniccomponent selected from a carbon material, a conductive polymericmaterial, and combinations thereof in a first liquid to form a firstdispersion; exposing a porous support structure to the first dispersion,whereby the electronic component remains on a surface of the poroussupport structure and the first liquid filters through the poroussupport structure; dispersing a negatively charged or chargeable lithiumion conducting component in a second liquid to form a second dispersion;and exposing the porous support structure to the second dispersion,whereby the negatively charged or chargeable lithium ion conductingcomponent remains on the surface of the porous support structure and thesecond liquid filters through the porous support structure.
 2. Themethod as defined in claim 1 wherein the method further comprises:mixing the first and second dispersions to form a single dispersion; andwherein the exposing steps are accomplished simultaneously by exposingthe porous support structure to the single dispersion.
 3. The method asdefined in claim 1 wherein the porous support structure is apolytetrafluoroethylene film, a polyethylene (PE) membrane, apolypropylene (PP) membrane, a membrane including a blend of PE and PP,or multi-layered structured porous films of PE and PP.
 4. The method asdefined in claim 1 wherein the porous support structure is a porouspolymer membrane, and the method further comprises allowing the porouspolymer membrane to remain in contact with the electronic component andthe negatively charged or chargeable lithium ion conducting, therebyforming a separator with the porous interlayer as a coating on theporous polymer membrane.
 5. The method as defined in claim 4 wherein theporous interlayer coating consists of: the electronic component; thenegatively charged lithium ion conducting component; and the electrolytefiling pores of the porous polymer separator and the porous interlayercoating.
 6. The method as defined in claim 4 wherein a percentage of thenegatively charged lithium ion conducting component in the porousinterlayer coating is 5 wt. % or less of a total wt. % of the porousinterlayer coating.
 7. The method as defined in claim 1 wherein thecarbon material is selected from carbon nanotubes, graphene, microporouscarbon, mesoporous carbon, hollow carbon spheres, and combinationsthereof; or the conductive polymeric material includes nanofibers,nanotubes, hollow spheres, or combinations thereof, the conductivepolymeric material being made of polypyrrole, polythiophene, orpolyaniline.
 8. The method as defined in claim 1 wherein the negativelycharged lithium ion conducting component is selected from negativelycharged sulfonated tetrafluoroethylene based fluoropolymer-copolymer,negatively charged polyacrylic acid, negatively charged sodium alginate,or a single lithium ion conductive polymer.
 9. A method for making aporous interlayer for a lithium-sulfur battery, the method comprising;dispersing an electronic component for conducting electrons in thelithium-sulfur battery selected from a carbon material, a conductivepolymeric material, and combinations thereof in a first liquid to form afirst dispersion; exposing a porous support structure to the firstdispersion, whereby the electronic component remains on a surface of theporous support structure and the first liquid filters through the poroussupport structure; dispersing a negatively charged or chargeable lithiumion conducting component for conducting lithium ions while repellingpolysulfides in the lithium-sulfur battery in a second liquid to form asecond dispersion; and exposing the porous support structure to thesecond dispersion, whereby the negatively charged or chargeable lithiumion conducting component remains on the surface of the porous supportstructure and the second liquid filters through the porous supportstructure to form the porous interlayer for the lithium-sulfur batterythat conducts electrons and lithium ions and repels polysulfides. 10.The method as defined in claim 9 wherein the porous support structure isa polytetrafluoroethylene film, a polyethylene (PE) membrane, apolypropylene (PP) membrane, a membrane including a blend of PE and PP,or multi-layered structured porous films of PE and PP.
 11. The method asdefined in claim 9 wherein the porous support structure is a porouspolymer membrane, and the method further comprises allowing the porouspolymer membrane to remain in contact with the electronic component andthe negatively charged or chargeable lithium ion conducting, therebyforming a separator with the porous interlayer as a coating on theporous polymer membrane.
 12. The method as defined in claim 11 wherein apercentage of the negatively charged lithium ion conducting component inthe porous interlayer coating is 5 wt. % or less of a total wt. % of theporous interlayer coating.
 13. The method as defined in claim 9 whereinthe carbon material is selected from carbon nanotubes, graphene,microporous carbon, mesoporous carbon, hollow carbon spheres, andcombinations thereof; or the conductive polymeric material includesnanofibers, nanotubes, hollow spheres, or combinations thereof, theconductive polymeric material being made of polypyrrole, polythiophene,or polyaniline.
 14. The method as defined in claim 9 wherein thenegatively charged lithium ion conducting component is selected fromnegatively charged sulfonated tetrafluoroethylene basedfluoropolymer-copolymer, negatively charged polyacrylic acid, negativelycharged sodium alginate, or a single lithium ion conductive polymer.